Infusion pump with a sealed drive mechanism and improved method of occlusion detection

ABSTRACT

A piston-type infusion pump is provided having an improved method of occlusion detection. The infusion pump includes processing circuitry for controlling the drive mechanism to infuse medication to a patient, including a sensor to track the position of the syringe plunger, thereby metering the amount of medication dispensed to the patient. The processing circuitry also includes a force sensor for providing signals indicative of the presence of occlusions along the infusion path. The operation of the drive mechanism causes delivery of medication to the patient. The infusion pump is constructed to be watertight.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of copending U.S. application Ser. No.09/335,999, filed Jun. 18, 1999 now U.S. Pat. No. 6,423,035 entitled:“Infusion Pump With A Sealed Drive Mechanism And Improved Method OfOcclusion Detection.”

BACKGROUND OF THE INVENTION

The present invention relates to an infusion pump for controlleddelivery of a pharmaceutical product to a subject, and more specificallyto an infusion pump having a sealed drive mechanism and improved methodof occlusion detection for determining the presence of obstructions inthe infusion path.

Infusion pumps provide a significant lifestyle benefit for individualsrequiring multiple deliveries of volumetrically proportioned medicationto their body over a period of time. Infusion pumps reliably dispensethe required medication to the patient through an infusion pathestablished between the patient and the pump. The infusion path is aconduit secured to the pump at one end and secured intravenously orsubcutaneously to a patient on the other. The operation of the infusionpump is controlled by a processor. The processor controls the deliveryof periodic dosages of medication to a patient at predetermined times.Thus, a patient is able to rely on the infusion pump for delivering therequired dosage of medication intravenously or subcutaneously over aperiod of time. In this way, the patient need not interrupt lifeactivities for repeated manual delivery of required medication.

As is known, infusion pumps often employ a piston-type drive mechanismfor urging the contents of a pharmaceutical cartridge or “syringe”internal to the pump along the infusion path to the subject. Piston-typeinfusion pumps are susceptible to an occlusion in the infusion path.Additionally, piston-type infusion pumps include complicated driveassemblies which require periodic maintenance and/or user adjustmentwhich further degrades the reliability of the device.

Most piston-type infusion pumps have an exposed lead-screw driveassembly that is manipulated by the user to reset the device each time anew syringe is inserted in the device. Because the lead screw is aprecision mechanical assembly that drives a plunger through the syringeto infuse pharmaceutical product along an infusion path, dirt and debrisin the exposed lead screw can cause the screw thread to either wear-downor lock-up at its point of engagement with a mated drive, either ofwhich can cause a pump failure. Some manufacturers suggest periodiccleaning of the lead screw, while the other manufacturers have equippedtheir devices with disposable lead screws and nut assemblies to preventsuch malfunctions. Installation of these parts in some pumps requirespartial disassembly of the device, further complicating syringeinstallation. Furthermore, many piston type infusion pumps are used withsyringe plungers manufactured with “O”-rings. The installation of thesyringe will often break the plunger seal about the O-ring and causemedication to leak through the plunger into the pump, possibly damagingelectrical components, but also causing medication not being deliveredproperly to the patients through infusion set electronics. Moreover,there is a need for an infusion pump with sealed and inaccessibleelectronics so the pump does not become damaged due to accidental ordeliberate submersion in water, and a sealed drive mechanism to preventdamage to the lead screw.

Often piston-type infusion pumps also do not show the amount ofmedication remaining in a syringe. Some manufacturers use a transparentwindow to visually inspect whether a syringe requires replacement. If apatient is not diligent about making such visual checks, he runs therisk of running out of medication. Other pumps indirectly determine theamount of remaining medication and, therefore, are subject toinaccuracies. Thus, there is a need for an infusion pump that directlyreports the amount of remaining medication.

While some infusion pumps are designed to subtract delivery volumes froma fixed full or a fixed half syringe volume, the amount of medication inthe syringe must be manually entered into the device at the outset bythe patient upon installation of the syringe, although it may actuallybe neither full nor half full initially. This requirement is still afurther complication of the syringe installation process.

Regarding occlusion detection, when an occlusion occurs anywhere alongthe infusion path of a piston-type pump, medication is not delivered tothe patient even though the piston moves to deliver the medication. Ascan be appreciated, the existence of an occlusion will prevent theinfusion pump from delivering medication to a patient until theocclusion is detected and cleared from the infusion path. Thus, therapid detection of occlusions along the infusion path is key to reliableoperation of a pump.

Presently, a piston-type infusion pump is desired which provides animproved method of occlusion detection, the pump including a simplifiedand reliable piston-type drive mechanism.

The present invention is directed to a piston-type infusion pump whichincludes an enclosed lead screw which can not be accessed withoutdisassembling the pump. Thus, the engagement and disengagement of drivemechanism are achieved remotely, by latching and unlatching of the pumpdoor, minimizing likely user error or abuse. The pharmaceutical syringehas a U-shaped plunger designed to link with the drive mechanism forsimple installation. Additionally, the pump displays exact amount ofmedication (i.e., insulin) remaining in the cartridge at any time andutilizes an improved method of occlusion detection.

BRIEF SUMMARY OF THE INVENTION

Briefly stated, the present invention provides a piston-type infusionpump having a remotely engaged piston-type drive mechanism and improvedmethod of occlusion detection. The internal components of the pump aresealed from the outside when a pharmaceutical syringe is installed, thuscreating a watertight seal when the pump is in its operational mode.

The infusion pump is designed to remotely engage and disengage the leadscrew of a drive mechanism by way of a latch stem, which is a part of apump door latching mechanism. The pump door latch has a watertightrotary seal between the casing of the infusion pump and the latch stem.When the pump door latch is moved up to allow the pump door to open, itdisengages the drive, so that the plunger of the syringe is free tomove. When the pump door latch is pushed down to lock the pump door ofthe infusion pump, it engages the drive. When in the locked position theplunger is moved only through rotation of the lead screw. Thus, theengagement and disengagement of drive mechanism are achieved remotely,by latching and unlatching of the pump door, minimizing likely usererror or abuse.

The infusion pump includes processing circuitry for controlling thedrive mechanism to infuse medication to a patient, including a sensor totrack the position of the syringe plunger. The sensor providesinformation that determines the volume of remaining insulin at any timein the pump. The infusion pump processing circuitry also includes aforce sensor and circuitry for uniquely processing signals indicative ofthe presence of an occlusion along the infusion path. The occlusiondetector operates with good accuracy at low volumes and delivery rates.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The foregoing summary, as well as the following detailed description ofpreferred embodiments of the invention, will be better understood whenread in conjunction with the appended drawings. For the purpose ofillustrating the invention, there is shown in the drawings embodimentswhich are presently preferred. It should be understood, however, thatthe invention is not limited to the precise arrangements andinstrumentalities shown.

In the drawings:

FIG. 1 is top view of the infusion pump with the top wall of the casingremoved to show the layout of the components in accordance with apreferred embodiment of the present invention;

FIG. 2 is a top view of the infusion pump shown in FIG. 1 with the pumpdoor open;

FIG. 3 is a front view of the pump door and latch assembly of theinfusion pump shown in FIG. 1 with the latch in the open position andthe pump door open for loading a syringe;

FIG. 4 is a front view of the infusion pump with the latch in the closedposition and the pump door closed with the pump housing a syringe;

FIG. 5 is a side view of the infusion pump with the pump door open;

FIG. 6 is a side view of the latch stem assembly with the latch in theclosed position and the pump door closed, with watertight seals inaccordance with a preferred embodiment of the invention;

FIG. 7 is a front view of the latch stem assembly with the latch in theopen position and the pump door open;

FIG. 8 is a front view of the lead screw and slide assembly in theengaged position in accordance with the preferred embodiment of FIG. 6;

FIG. 9 is a front view of the lead screw and slide assembly in thedisengaged position in accordance with the preferred embodiment of FIG.6;

FIG. 10 is a top view of the lead screw and slide assembly engaging asyringe in the infusion pump in accordance with the preferred embodimentof FIG. 6;

FIG. 11 is a side perspective view of the syringe and plunger assembly;

FIGS. 12a and 12 b are block diagrams of the circuitry of the infusionpump in accordance with the preferred embodiment of FIG. 10;

FIG. 13 is a flow chart of a preferred system failure detection methodemployed by the circuitry of FIGS. 12a and 12 b;

FIG. 14 is a graph of force v. time showing the sampling of force dataprior to the initiation of a delivery cycle;

FIGS. 15-19 are flow charts showing individual system failure detectionmethods in accordance with the preferred method of FIG. 13.

DETAILED DESCRIPTION OF THE INVENTION

Certain terminology is used in the following description for convenienceonly and is not limiting. The words “right,” “left,” “lower” and “upper”designate directions in the drawings to which reference is made. Thewords “inwardly” and “outwardly” refer to directions toward and awayfrom, respectively, the geometric center of the infusion pump anddesignated parts thereof. The terminology includes the wordsspecifically mentioned above, derivatives thereof and words of similarimport.

The term “Bolus” as used herein refers to a dosage of medication whichis large with respect to typical dosage levels. For example, wheninfusing insulin to a patient over a period of time, a bolus istypically delivered to a patient before or during a meal to compensatefor the increased amount of insulin required to balance glucose producedby food, or when the blood glucose is high. “Basal” as used hereinrefers to the essential dosage of medication which must be delivered toa patient repeatedly over a period of time to maintain normal biologicalfunction.

Referring to FIG. 1, a piston-type infusion pump 5 in accordance withthe present invention is shown for delivering medication 24 to a patientalong an infusion path 14. The infusion pump 5 includes a sealed pumpcasing 7, processing circuitry 200, power cells 70, force sensor 16, LED207, optical linear sensor 208, motor 10, lead screw 15, half nut 18,slide 22, syringe 12, gear train 28, and infusion path 14.

In operation, processing circuitry 200, powered by power cells 70,controls the operation of the infusion pump 5. The motor 10 isincrementally engaged to infuse medication to a patient at predeterminedintervals. Upon engagement, the motor 10 causes the lead screw 15 torotate by means of the gear train 28. When the half nut 18 is engagedwith the lead screw 15 and the lead screw 15 is driven by the motor 10,the slide 22 traverses the slide rail 72 (see FIGS. 8-9) pushing theplunger 20 of the syringe 12. This causes delivery of medication 24 atthe distal end 26 of the syringe 12. An infusion path 14 to deliver themedication 24 is connected by the connector 27 to the dispensing tip 25of the syringe 12 to provide fluidic communication between the infusionpump 5 and a patient.

Referring now to FIGS. 2-5, the casing of the infusion pump 5 is shown.The pump casing 7 is preferably formed of a thermoplastic material andpreferably made watertight by sealing any openings in the pump casing 7.The watertight pump casing 7 of FIGS. 2-5 preferably prevents damage toany components contained inside it. The pump casing 7 supports LCDdisplay 30, keypad 42, priming button 44, battery door 40, exteriorinfusion port 46, hinge 38, pump door latch 48, and pump door 36.

LCD display 30 is a menu driven graphic display. In this embodiment thedisplay items are listed vertically allowing the patient to scrollthrough menus until finding the desired item to access status data or toprogram the infusion pump 5. Other display configurations of the LCDdisplay 30 are possible in other embodiments, as well as the ability todisplay other information on the LCD display 30.

FIGS. 2-5 show the syringe loading process. In FIGS. 2 and 3, the pumpdoor 36 is opened to expose the interior infusion port 50 and thebattery door 40. The syringe 12 is installed through interior infusionport 50, interior to the pump casing 7 of the infusion pump 5, creatinga watertight seal. In FIGS. 2 and 3, the pump door latch 48 has beenrotated away from the pump casing 7 in order to release the pump door 36so it may pivot open at hinge 38. The release of pump door 36 enablesthe patient to rotate the pump door 36 about the hinge 38 therebyexposing interior infusion port 50 as shown in FIG. 3. Interior infusionport 50 is provided to receive a syringe 12 containing a supply ofpharmaceutical product to be infused along the infusion path 14 by theinfusion pump 5 as best shown in FIG. 10. The battery door 40 is removedfor replacing the power cells 70. The battery door 40 preferably snapsinto place and preferably includes a seal to maintain the watertightproperties of the pump casing 7.

The syringe 12 ideally includes a plunger 20 and a plunger stem 21 forengagement with the slide 22 upon installation in the interior infusionport 50 (see FIG. 1). The syringe 12 is installed in the infusion pump 5by rotating the pump door latch 48 away from the pump door 36 of theinfusion pump 5 as shown in FIGS. 3 and 5. The pump door 36 is thenrotated away from the infusion pump 5 about the hinge 38, exposing theinterior infusion port 50, which receives the syringe 12. The pump door36 closes in the opposite manner of opening, and the pump door latch 48is rotated back into place, locking the pump door 36 as shown in FIG. 4.

Referring now to the preferred embodiment of FIGS. 6 and 7, there ispreferably an elastomeric O-ring 52 assembled on the inside diameter ofinterior infusion port 50. The O-ring 52 provides a seal between thepump casing 7 and the syringe 12. When the syringe 12 is installed inthe interior infusion port 50 of the pump casing 7, the pump door 36 isclosed and latched in place by rotating the pump door latch 48 over thepump door 36. As pump door 36 is closed, the syringe 12 is pushedagainst the pump casing 7 as shown in FIG. 6, and the O-ring 52 issqueezed in the interior infusion port 50 creating a seal at the distalend 26 of the syringe 12. The interior infusion port 50 is preferablythe only opening in the pump casing 7. Thus the inside of the pumpcasing 7 is preferably sealed from outside contaminants, creating awatertight seal.

Pump door latch 48 is fixedly mounted on latch stem 62 which extendsalong the interior length of the interior of pump casing 7. The axis oflatch stem 62 is parallel with the longitudinal axes of syringe 12 andlead screw 15. The latch stem 62 is held in the wall of pump casing 7 bya rotary seal 54. Seal 54 is held in place by bias spring 55 and washer58, which are held in place over latch stem 62 by collar 56. Uponrotation of pump door latch 48 to secure the syringe 12 within interiorinfusion port 50, the translation of the pump door latch 48 to theclosed position causes a rotation of the latch stem 62. Rotation oflatch stem 62 moves the half nut 18 into engagement with the lead screw15 as shown in FIGS. 8 and 9.

FIGS. 8 and 9 show the mechanism for the preferred embodiment of FIG. 6that engages and disengages the half nut 18 to the lead screw 15 throughrotation of the pump door latch 48 and latch stem 62. The lead screw 15is mounted on a carriage 64 (the carriage 64 mounted to the pump casing7) so as to be parallel with latch stem 62. The half nut 18 is attachedto the slide 22. In FIG. 8, when the pump door latch 48 is moved to lockthe pump door 36, it also rotates latch stem 62 to disengage cam 63 fromnut lever 68, and moves the half nut 18 to engage the lead screw 15. Thespring 66 is anchored to the half nut 18 and to the slide 22 as shown.Spring 66 holds the half nut 18 to the right side of the axis X when thecam 63 releases the nut lever 68, thereby holding the half nut 18 in theengaged position.

Likewise, in FIG. 9, when the pump door latch 48 is rotated away fromthe pump door 36 to unlock the pump door 36, it also turns the latchstem 62. Cam 63 consequently pushes down on the nut lever 68 and, hencemoves the half nut 18, to the disengaged position, where it is held onthe left side of the axis X by the spring 66. This releases the slide 22to move to any position along the slide rail 72 when pushed by theplunger stem 21 of syringe 12. The lead screw 15, latch stem 62, theslide 22 and the half nut 18 are all preferably sealed internalcomponents to the pump 5 and are not accessed by the user.

A buttress thread is preferably used for the lead screw 15 and the halfnut 18, since the lead screw 15 engages and pushes the half nut 18 onlyin one direction. The wear components e.g., the lead screw 15 and thehalf nut 18 are preferably coated with a low friction, wear resistantcoating to prolong life and to reduce power required to drive theinfusion pump 5.

FIGS. 8 and 9 also show how the amount of medication 24 remaining in thesyringe 12 can be determined by the processing circuitry 200 at anygiven time. A light source, LED 207 is mounted on the slide 22. Anoptical linear sensor 208 is fixedly mounted to the carriage 64. Theposition of the slide 22 can be accurately measured at any moment by theoptical linear sensor 208 by determining location of the LED 207relative to the sensor 208. The position of the slide 22 also determinesthe position of the plunger 20. Since the diameter and position of thesyringe 12 are known, based on the position of the slide 22, the amountof medication 24 remaining in the syringe 12 can also be determined bythe processing circuitry 200 as described herein.

Referring now to FIG. 11, a syringe 12 for use with the infusion pump 5is shown. The syringe 12 includes a plunger 20 which preferably includesa generally elongated, “cup-shaped” plunger stem 21 and a dispensing tip25. In FIG. 10 the plunger stem 21 contacts the slide 22 so that theslide 22 may push the plunger stem 21 when engaged by the half nut 18and urged by the lead screw 15. The plunger stem 21 is preferablycup-shaped so that the lead screw 15 may reside within the cavitycreated by the plunger stem 21, without exerting any pressure on theplunger 20 or the plunger stem 21. The slide 22 includes an aperture 23(see FIGS. 8 and 9), larger than the diameter of the lead screw 15, suchthat the lead screw 15 passes through the slide 22 to engage the halfnut 18 and the gear train 28. Upon installation of the syringe 12 in theinterior infusion port 50 of the pump casing 7, the plunger 20 normallyadvances the slide 22 axially away from the exterior infusion port 46along the slide rail 72. The slide 22 is free to move, because, when thepump door 36 is open, the half nut 18 is rotated out of engagement withthe lead screw 15.

In operation, the patient primes the infusion pump 5 to remove air fromthe infusion path 14 by depressing the priming button 44 until theinfusion path 14 is free from air bubbles. In priming mode, the motor 10drives medication 24 along the infusion path 14 until the patient issatisfied that the infusion path 14 is clear of air. Once the infusionpump 5 is primed the device is ready for programmed operation for abasal rate or bolus operation depending on the patient's requirements.

In programmed operation, the motor 10 causes the lead screw 15 to rotateby means of the gear train 28. When the half nut 18 engages the leadscrew 15 and the lead screw 15 is driven by the motor 10, the rotationof the lead screw 15 moves the half nut 18 and the slide 22 traversesthe slide rail 72 pushing the plunger 20 of the syringe 12. This causesdelivery of medication 24 at the distal end 26 of the syringe 12. Aninfusion path 14 is linked to exterior infusion port 46 to deliver themedication 24 to a patient.

Processing Circuitry

Referring now to FIGS. 12a and 12 b, a block diagram of processingcircuitry 200 of the preferred embodiment of the infusion pump 5 isshown. Processing circuitry 200 includes: processor 220, power section205, force sensor section 225, position sensor section 245, motor drivesection 270, as well as additional interface and signal conditioningcircuitry described hereinafter.

Power section 205 preferably includes three sources of power for theinfusion pump 5, although other embodiments may utilize different powerconfigurations. In the preferred embodiment of FIGS. 12a and 12 b Vbatt1and Vbatt2 (power cells 70 in FIG. 1) are each preferably 2 silver oxidebatteries in series. Vlithium is a backup source when Vbatt1 and Vbatt2are low or are being replaced. Power section 205 is connected to theprocessing circuitry 200 by diode 212. Vlithium provides enough power tokeep the system clock circuit 288 running. Vbatt1 provides power to the3.3 Volt DC-DC regulator 214. The regulator 214 provides 3.3V to theprocessing circuitry 200 with the exception of the LCD module 218.Vbatt2 provides power to the motor drive 272 and the LCD module 218. Theprocessor 220 switches the 3.3V power to the various sub-systems as theyrequire power.

In an alternative embodiment, Vlithium is not used, and instead the 32KHz clock 288 is replaced by a lower power real time clock (RTC)circuit. The RTC is powered by the 3.3V regulator through a diode. Whenthe batteries are low or they are being replaced the RTC will be poweredfrom a charge stored in a capacitor.

A power converter 286 provides −3.3V and +5.2V as needed by varioussubsystems.

Processor and Support Circuits

The processor 220 is a microprocessor or microcontroller integrated withmemory and peripherals. The processor 220 preferably operates at 8 MHz.This is supplied from a quartz crystal (not shown). The processor 220monitors the force sensor section 225 and the position sensor section245 and controls the motor drive section 270 in accordance with aninstruction set as described below. The processor 220 also determinesthe battery voltages and will alarm the user when it is time to replacethe batteries through the audible beeper 280 and/or LCD module 218. A 32KHz signal is also generated by system clock circuit 288 which is usedwhen the processor 220 is placed in sleep mode. If the circuit power(3.3V from the regulator 214) drops below a threshold, the processor 220will be placed in reset by under voltage circuit 300.

Serial communications circuit 290 is an RS-232 port. The serialcommunications circuit 290 is provided for test purposes.

Keypad circuit 289 is an interface which allows the user, through keypad42, to program the infusion pump 5, view status and history, deliver abolus and turn on a back light for the LCD display 30.

The LCD module 218 consists of LCD display 30 and graphicscontroller/driver and backlighting. The graphics controller/driverintegrated circuit is controlled through a parallel interface (notshown) from the processor 220. A 2 KHz clock signal is provided to theLCD module 218 by system clock circuit 288; Vbatt2 provides the power toLCD module 218.

A watchdog timer 284 is used to ensure that the pump motor 10 is stoppedif the instruction set of processor 220 has lost control of the infusionpump 5 or if a diagnostic test fails.

The non-volatile memory 282 is preferably an EEPROM used to store userprogrammable variables and pump history data for use by the instructionset of processor 220.

Force Sensor Section

Force sensor section 225 includes FSR circuit 230 (including forcesensor 16), reference voltage circuit 227, and amplifier circuit 229.

A DC motor 10 of the infusion pump 5 drives the lead screw 15 thatdrives the plunger 20 of syringe 12 to deliver medication 24 to apatient along the infusion path 14. An FSR (force sensitive resistor)circuit 230, through force sensor 16, is used to sense the force on thelead screw 15 prior to the initiation of the delivery cycle. If there isan occlusion (an obstruction in the infusion path 14) the force on forcesensor 16 will increase and will be detected by the processor 220.Similarly, if there is a leakage or absence of the syringe 12 within theinfusion pump 5, the force sensor 16 will reflect a low force value. Theprocessor 220 will alarm the user through audible beeper 280 and/or LCDmodule 218.

A 2.5V reference is supplied to the FSR circuit 230 and the output isamplified by amplifier circuit 229 before it is digitized by theprocessor 220. The processor 220 monitors the force and applies analgorithm (as described herein) to detect if an occlusion has occurred.

Position Sensor

Position Sensor Section 245 includes linear sensor circuit 244, andamplifier circuit 242.

An optical linear sensor 208 of linear sensor circuit 244, such as alinear sensor manufactured by Hamamatsu Corp., is used to track themotion of the plunger 20. The main function of the optical linear sensor208 is to provide information that determines the volume of medication24 remaining in the infusion pump 5 at any time. The linear sensorsignal is also used to monitor any gross inaccuracy in medication 24delivery by calculating delivery volume between any two points of time.

The optical linear sensor 208 is attached to the infusion pump 5 in aknown, fixed position. The LED 207 of linear sensor circuit 244 isattached to the slide 22 that is moved to push the plunger 20 to causedelivery of medication 24. By knowing the position of the LED 207, theprocessor 220 calculates the position of the plunger 20. Since thesyringe 12 is of a known diameter and is in a fixed position in theinfusion pump 5, the position of the plunger 20 is used to determine thevolume of remaining medication 24 in the syringe 12 at any time.

The optical linear sensor 208 of linear sensor circuit 244 is preferablya two electrode photo-diode device that provides continuous positiondata of light spots traveling over its surface. The current at eachelectrode of the optical linear sensor 208 is inversely proportional tothe distance of the light source from the electrode. When the LED 207 ispulsed on, the current from each electrode of the optical linear sensor208 is inversely proportional to the distance of the LED 207; by usingtwo electrodes, errors due to power fluctuations can be minimized. Theelectronic pulses on the LED 207 cause current to flow from each of thesensor's electrodes. The currents are fed into trans-impedanceamplifiers 242 and the processor 220 reads and digitizes the amplifiedcurrent and applies an algorithm to determine and monitor the positionof the plunger 20.

For example, in the preferred embodiment, the algorithm used todetermine the medication 24 remaining (based on 300 units in a fullsyringe of U100 concentration insulin):

Units=G 1[A−B]/[A+B]+[150−K 1]

G1=[37/25.5778]*150

A=8 bit digitized value of sensor A output

B=8 bit digitized value of sensor B output

K1=offset value from calibration routine

or=G1[Acenter-of-travel−Bcenter-of-travel]/[Acenter-of-travel+Bcenter-of-travel]

Motor Drive

Motor drive section 270 includes motor circuit 278, encoder circuit 274,and amplifier circuit 276.

The output of an integrated DC motor 10 of motor circuit 278, encoderand gear reducers are used to drive the lead screw 15 that moves theplunger 20 of the infusion pump 5. The motor 10 is driven by a PWM(pulse width modulated) signal which is provided by the processor 220.

The motor 10 of motor circuit 278 is a closed loop velocity control withthe feedback signal being the back-EMF of the motor which is amplifiedby the amplifier circuit 276. The closed loop control algorithm is aproportional type of control. The motor 10 is commanded to a constantspeed and the processor 220 counts the pulses from the encoder circuit274. When the motor 10 has moved the required number of pulses, the PWMsignal from the processor 220 is turned off and a brake is applied. Onthe next maneuver the processor 220 will compensate for any undershootor overshoot of the previous maneuver. For a basal delivery the motor 10will move the lead screw 15 every 3 minutes. For the minimum requiredbasal rate of 0.1 units/hr (1 microliter/hr) this means 0.005 units or0.05 microliters is delivered every 3 minutes.

Referring now to FIG. 13 (and the respective step numbers), a method ofdetecting an occlusion or leakage in the infusion path 14 of theinfusion pump 5 is shown. FIGS. 15-19 show the individual methods ofocclusion and leakage detection which the infusion pump 5 utilizes. Whenan occlusion or leakage occurs anywhere in the infusion path 14,medication 24 is not properly delivered to the patient. The extra volumeof medication not delivered to the patient must occupy space within theinfusion path 14 or the syringe 12. The infusion path 14 and syringe 12are preferably made of semi-rigid or semi-flexible plastic. An increasein medication volume causes an increase in pressure within themedication fluid which can be monitored as force incident on the forcesensor 16 at the end of the lead screw 15. As such, where medication 24is frequently delivered (e.g., basal delivery every 3 minutes), thispressure increases with each delivery if the infusion path 14 is andremains occluded. Thus, the force sensor 16 located at the end of thelead screw 15 will encounter increased force prior to every deliverycycle of medication if there is an occlusion present in the infusionpath 14.

At the outset of a delivery cycle, step 1 in FIG. 13, the processor 220reads the signal of the force sensor circuit 230 which indicates theamount of force (FN) incident to the force sensor 16. The signal FN ispassed to the processor 220 and is then compared to a reference value instep 2, FMAX, in this example, 2 volts. This process (see FIG. 15) willdetect an occlusion in the system, since in all cases the FN readingshould be less than the reference value. The reference value FMAX isstored in the non-volatile memory 282 of the processing circuitry 200.If the signal FN is greater than this value, an occlusion is present andthe audible beeper 280 is sounded in step 6. Otherwise the process movesto step 3.

In step 3 of FIG. 13 (see also FIG. 16), the force signal FN is comparedto a minimum threshold reference value to determine whether or not asyringe 12 having medication 24 is properly loaded in the infusion pump5. This minimum reference value, FLEAK, is also stored in the memory 282of the processing circuitry 200. If the signal FN at the force sensor 16does not exceed the minimum threshold, the alarm is sounded in step 6.Such a condition also indicates possible leakage in the infusion pump 5or in the infusion path 14 or the absence altogether of a syringe 12 inthe infusion pump 5.

For the lowest basal rate the force signal FN does not always increaseunder occlusion conditions. This is because, at such a low basal rate,the increase in force due to occlusion is sometimes less than thevariation in the force signal FN due to the drive mechanism turning thelead screw 15. Thus, a particular method is required to detect anocclusion if an extremely low basal rate is being used. In step 4 ofFIG. 13 (see also FIG. 17), the processor 220 determines the presentbasal rate. If the rate is less than the predetermined threshold, BMIN,the process proceeds to step 7.

As shown in step 7 of FIG. 13, for a low basal rate, the force signalvalue FN is compared to a stored minimum value, FMIN. If the forcesignal FN is greater than FMIN the process proceeds to step 12. In step12 the amount by which FN exceeds FMIN is determined. If the amount thatFN exceeds FMIN (FN−FMIN) is greater than a predetermined threshold,FINC (here 0.1 volts), an occlusion has been detected, and the processproceeds to step 6 to sound the audible beeper 280; if FN does notexceed FMIN by the predetermined threshold FINC (i.e., FN−FMIN is lessthan 0.01), the process proceeds to step 11 and delivers medicine 24along the infusion path 14 by incrementally moving the plunger 20.

In step 7 of FIG. 13, if FN is less than a stored minimum value FMIN,step 9 stores the current value of FN as the new FMIN in the memory 282and the process proceeds to step 11 to delivers medication 24 along theinfusion path 14 by incrementally moving the plunger 20.

If step 4 determines that the basal rate is greater than a predeterminedrate, the process proceeds to step 8 (see also FIG. 18). In step 8, FNis compared to the force signal from the previous delivery cycle,FN(n−1), stored in the memory 282. If in step 8 FN is greater thanFN(n−1), a counter is incremented in step 13 to record an instance ofincreasing pressure from FN(n−1) to FN. If in step 14 the counter showsincreasing pressure for a predetermined number (greater than 1) ofcycles, an occlusion is declared and the beeper 280 is sounded in step6. Otherwise the process proceeds to step 11 and delivers medication 24along the infusion path 14 by incrementally moving the plunger 20.

If the signal FN in step 8 does not exceed FN(n−1), the counter is resetto zero in step 10 and the process proceeds to step 11 to delivermedication 24 along the infusion path 14 by incrementally moving theplunger 20.

FIG. 19 reflects an occlusion detection method whereby step 8 comparesFN to the force signal from the previous delivery cycle, FN(n−1). If theFN is greater than FN(n−1) by a predetermined maximum amount, FLIMIT,the beeper is sounded in step 6 without incrementing or checking thecounter in step 13. If FN is not greater than FN(n−1) by FLIMIT, thecounter is reset to zero in step 10 and the process proceeds to step 11.

Prior to initiating the delivery cycle over again, the processorproceeds to step 15 to wait until a predetermined time has passed.

Thus, the infusion pump 5 determines the presence of an occlusion in theinfusion path 14 by processing force measurements from the force sensor16 if one of the following occurs:

If the force measured during a delivery cycle, at a point immediatelybefore the start of the subsequent delivery of medication, is greaterthan the force at the identical point in the previous cycle, and hasbeen so for a predetermined number of delivery cycles, i.e.:

F 1<F 2<F 3<F 4, . . . FN(n−1)<FN for a predetermined number of cycles.

If the force measured during a delivery cycle, at a point immediatelybefore the start of the subsequent delivery of medication, is greaterthan the force at the identical point in the previous cycle by an amountgreater than a predetermined value, i.e.:

FN−FN(n−1)>FLIMIT.

If, in situations using low basal rates, the difference in force valuetaken during a cycle, at a point immediately before the start of thesubsequent delivery of medication, and the force value at an identicalpoint from any previous cycle for low basal rates, is greater than apredetermined value, i.e.:

(FN−FMIN)>a predetermined value, FINC.

If the force measured during a cycle, at a point immediately before thestart of the subsequent delivery of medication is greater than apredetermined value, i.e.:

FN>a predetermined value, FMAX.

The force measurements are also used to detect if the syringe 12 isremoved, or if the infusion path 14 is not connected to exteriorinfusion port 46. In these cases the force measured will be close tozero and the infusion pump 5 will alarm the user to check the syringe 12and infusion path 14 for possible leakage or other condition.

Referring now to FIG. 14, a graph of four sequential force signalsduring an occlusion condition are shown. The force v time relation of anocclusion is apparent from the figure, as the amount of forceimmediately preceding each delivery cycle is shown as higher than thepreceding cycle, indicating the presence of an occlusion in the infusionpath 14. FIG. 14 represents the condition which the method of FIG. 18detects.

It will be appreciated by those skilled in the art that changes could bemade to the embodiments described above without departing from the broadinventive concept thereof. It is understood, therefore, that thisinvention is not limited to the particular embodiments disclosed, but itis intended to cover modifications within the spirit and scope of thepresent invention.

We claim:
 1. An occlusion detector for use with an infusion pump fordispensing volumetrically proportioned doses of pharmaceutical productto a patient, the infusion pump having a pharmaceutical storage area forcontaining a supply of pharmaceutical product and adapted to beconnected to, an infusion path between the storage area and the patient,an incrementally operated urging mechanism for urging contents of thestorage area to infuse a volumetrically proportioned dose of thecontents along the infusion path to the patient, the urging mechanismtraveling a complete increment in a delivery cycle, and a drivemechanism operably linked to the urging mechanism to control theincremental movement of the urging mechanism for dispensing avolumetrically proportioned dose of pharmaceutical product to thepatient by way of the infusion path, the occlusion detector comprising:a force transducer which provides a signal representative of forceincident to the urging mechanism within the storage area; a memory whichstores information representative of the transducer signal; a processorconnected to the force transducer which monitors and receives the forcetransducer signal prior to a delivery cycle and actuation of the drivemechanism for dispensing of pharmaceutical product along the infusionpath, the signal defined as a cycle signal, stores informationrepresentative of the cycle signal in the memory, compares a currentcycle signal level to a previous cycle signal level stored in the memoryand determines whether the current cycle signal level has increased overthe previous cycle signal level to identify an increase in forceincident to the urging mechanism within the storage area; and an alarmto alert the patient, triggered by the processor upon the identificationof a predetermined number of increasing cycle signal levels whereby theincreasing signal levels indicate an occlusion in the infusion path. 2.The occlusion detector of claim 1 wherein the processor monitors theforce transducer immediately prior to actuation of the drive mechanism.3. The occlusion detector of claim 2 wherein the processor compares abasal rate of the infusion to a predetermined basal rate prior tocomparing the cycle signal levels.
 4. The occlusion detector of claim 3wherein cycle signal levels below the predetermined basal rate ofinfusion are compared to a predetermined signal value and cycle signallevels exceeding said predetermined signal value by a predeterminedamount trigger the alarm.
 5. A method of detecting an occlusion along aninfusion path of an infusion pump having a pharmaceutical storage areafor containing a supply of pharmaceutical product, and adapted to beconnected to the infusion path between the storage area and a patient,an incrementally engaged urging mechanism for urging contents of thestorage area to infuse a volumetrically proportioned dose of thecontents along the infusion path to the patient, a force transducer forproviding a signal representative of the force incident to the urgingmechanism within the storage area, and a drive mechanism operably linkedto the urging mechanism to control the incremental movement of theurging mechanism for dispensing a volumetrically proportioned dose ofpharmaceutical product to the patient by way of the infusion path, themethod comprising: monitoring the signal of the force transducer priorto delivery cycles and the actuation of the drive mechanism fordelivering a dose of pharmaceutical product to the patient, the signaldefined as a cycle signal; storing information representative of thecycle signals of the force transducer in a memory; comparing a currentcycle signal of the force transducer to a previous cycle signal storedin the memory for identifying an increase in force incident to theurging mechanism within the storage area; determining whether thecurrent cycle signal level has increased over the preceding cycle signallevel; counting each such increase; and activating an alarm when apredetermined number of force increases have been counted.
 6. The methodof claim 5 wherein the alarm is activated upon monitoring apredetermined number of sequential cycle increases.
 7. The method ofclaim 5 further comprising the step of comparing the cycle signals to apredetermined value and activating the alarm if a cycle signal isgreater than the predetermined value.
 8. The method of claim 5 furthercomprising the step of comparing the cycle signals to a predeterminedvalue and activating the alarm if a cycle signal is less than thepredetermined value.
 9. The method of claim 5 wherein the monitoringfunction is performed by a processor.
 10. A method of detecting anocclusion along an infusion path of an infusion pump having apharmaceutical storage area for containing a supply of pharmaceuticalproduct adapted to be connected to the infusion path between the storagearea and a patient, an incrementally operated urging mechanism forurging contents of the storage area to infuse a volumetricallyproportioned dose of the contents along the infusion path to thepatient, a force transducer for providing a signal representative of theforce incident to the urging mechanism within the storage area, and adrive mechanism operably linked to the urging mechanism to control theincremental movement of the urging mechanism for dispensing avolumetrically proportioned dose of pharmaceutical product to thepatient by way of the infusion path, the method comprising: monitoringthe signal of the force transducer prior to delivery cycles and theactuation of the drive mechanism for delivering a dose of pharmaceuticalproduct to the patient, the signal defined as a cycle signal; storinginformation representative of the force transducer cycle signal in amemory; comparing a current cycle signal of the force transducer to aprevious cycle signal stored in the memory for identifying an increasein force incident to the urging mechanism within the storage area;determining whether the current cycle signal level has increased overthe preceding cycle signal level by an amount greater than apredetermined value; and activating an alarm when the current cyclesignal has increased over the preceding cycle signal by an amountgreater than the predetermined value.
 11. A method of detecting anocclusion along an infusion path of an infusion pump having apharmaceutical storage area for containing a supply of pharmaceuticalproduct adapted to be connected to the infusion path between the storagearea and a patient, an incrementally engaged urging mechanism for urgingcontents of the storage area to infuse a volumetrically proportioneddose of the contents along the infusion path to the patient, a forcetransducer for providing a signal representative of the force incidentto the urging mechanism within the storage area, and a drive mechanismoperably linked to the urging mechanism to control the incrementalmovement of the urging mechanism for dispensing a volumetricallyproportioned dose of pharmaceutical product to the patient by way of theinfusion path, the method comprising: monitoring the signal of the forcetransducer prior to delivery cycles and the actuation of the drivemechanism for delivering a dose of pharmaceutical product to thepatient, the signal defined as a cycle signal; determining whether thebasal rate of the pharmaceutical delivery is less than a predeterminedrate; determining whether a current cycle signal for a basal rate lessthan the predetermined rate is less than a predetermined minimum value;comparing the cycle signal of the force transducer to the predeterminedminimum value; determining whether the current cycle signal level hasincreased over the predetermined minimum value by more than apredetermined amount; and activating an alarm upon the determination ofa force increase above the predetermined amount.
 12. A system faultdetector for use with an infusion pump for dispensing volumetricallyproportioned doses of pharmaceutical product to a patient, the systemfault detector comprising: a force transducer which provides signalsrepresentative of a force incident to an urging mechanism within theinfusion pump; and a processor which controls the urging mechanism andmonitors the signals from the force transducer prior to a plurality ofpump delivery cycles, wherein the processor stores informationrepresentative of the signals from the force transducer in a memory forthe plurality of delivery cycles, receives a current force signal of acurrent delivery cycle from the force transducer immediately prior toactuating the drive mechanism during a delivery cycle, compares thecurrent force signal to a previous force signal of a previous deliverycycle, determines whether the current force signal represents a forceincrease over the previous force signal, counts the number of sequentialforce increases between pump delivery cycles, and activates an alarmupon identification of a predetermined number of force increases. 13.The system fault detector of claim 12 wherein the processor furthercompares a current basal rate of infusion to a predetermined basal rateprior to comparing the current force signal to the previous forcesignal, and wherein the processor compares the current force signal to apredetermined minimal signal level if the basal rate of infusion isbelow the predetermined basal rate of infusion, and triggers an alarm ifthe current force signal exceeds the pregetermined minimal signal levelby a predetermined amount.
 14. The system fault detector of claim 12wherein the processor further compares the current force signal to apredetermined maximum value and triggers the alarm if the current forcesignal is greater than the predetermined maximum value.
 15. The systemfault detector of claim 12 wherein the processor further compares thecurrent force signal to a predetermined minimum value and triggers thealarm if the current force signal is less than the predetermined minimumvalue.
 16. The system fault detector of claim 12 wherein the processorfurther compares the current force signal to the previous force signaland triggers the alarm if the current force signal is greater than theprevious force signal by a predetermined value.
 17. A method ofdetecting an occlusion along an infusion path and/or within a storagearea of an infusion pump, the method comprising: monitoring signals froma force transducer prior to a plurality of pump delivery cycles, todetect the force incident to an urging mechanism within the infusionpump; storing information representative of the force signals in amemory for the plurality of delivery cycles; comparing a force signalfor a current delivery cycle to a force signal for a previous deliverycycle to determine whether the force signal for the current deliverycycle represents a force increase over the force signal for the previousdelivery cycle; counting the number of sequential increases in forcebetween pump delivery cycles; and activating an alarm when apredetermined number of force increases have been counted.
 18. A methodof detecting an occlusion along an infusion path and/or within a storagearea of an infusion pump, the method comprising: monitoring signals froma force transducer prior to a plurality of pump delivery cycles, todetect the force incident to an urging mechanism within the infusionpump; storing information representative of the force signals in amemory for the plurality of pump delivery cycles; comparing a forcesignal for a current delivery cycle, defined as a current force signal,to a force signal for a previous delivery cycle, defined as a previousforce signal, to determine whether the current force signal represents aforce increase over the previous force signal by an amount greater thana predetermined value; and activating an alarm if the current forcesignal has increased over the previous force signal by an amount greaterthan the predetermined value.
 19. A method of detecting an occlusionalong an infusion path and/or within a storage area of an infusion pump,the method comprising: monitoring signals from a force transducer priorto a plurality of pump delivery cycles, to detect the force incident toan urging mechanism within the infusion pump; determining whether thebasal rate of a current delivery cycle is less than a predeterminedrate; if the basal rate is less than the predetermined rate, determiningwhether a force signal for the current delivery cycle, defined as acurrent force signal, represents a force level less than a minimum forcelevel; if the current force signal is less then the minimum force level,storing the current force signal in a memory as the minimum force level;if the current force signal is greater than the minimum force level,determining if the current force signal represents a force level higherthan the minimum force level by an amount greater than a predeterminedforce increase value; and activating an alarm upon determination of aforce increase greater than the predetermined force increase value. 20.A method of detecting an occlusion along an infusion path and/or withina storage area of an infusion pump, the method comprising: monitoringsignals from a force transducer prior to a plurality of pump deliverycycles, to detect the force incident to an urging mechanism within theinfusion pump; comparing a force signal for a current delivery cycle toa predetermined maximum value; and activating an alarm if the forcesignal for the current delivery cycle exceeds the predetermined maximumvalue.
 21. A method of detecting leakage along an infusion path and/orwithin a storage area of an infusion pump, the method comprising:monitoring signals from a force transducer prior to a plurality of pumpdelivery cycles, to detect the force incident to an urging mechanismwithin the infusion pump; comparing a force signal for a currentdelivery cycle to a predetermined minimum value; and activating an alarmif the force signal for the current delivery cycle is less than thepredetermined minimum value.